1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus which forms images on a recording medium by ejecting droplets of ink onto the recording medium.
2. Description of the Related Art
The inkjet type image forming apparatus forms images on a recording medium by ejecting droplets of ink from nozzles toward the recording medium, such as a sheet of paper, while relatively moving the recording medium and an ink droplet ejection head having an arrangement of a plurality of nozzles (apertures).
In recent years, improvements in image quality have been sought in image forming apparatuses by increasing the density of the nozzles of the apparatuses. Generally, the ink used in the image forming apparatus of this kind contains a large volume of liquid solvent, such as water, organic solvent, or the like.
If the recording medium is a permeable medium in which the ink permeates the interior of the medium, then unless the solvent component in the ink deposited on the recording medium is not sufficiently removed, so-called “bleeding” can arise as the ink permeates the recording medium. The bleeding includes problems such as that the dot size becomes larger than the prescribed diameter, the boundary regions of the dots become blurred, the spreading of the dots becomes uneven, or the outline of each dot does not become smooth.
If the recording medium is a non-permeable medium in which the ink becomes fixed principally on the surface of the medium, then unless the solvent component in the ink deposited on the recording medium is not sufficiently removed, it is not possible to stably fix the coloring material component in the ink on the surface of the recording medium.
Therefore, various types of image forming apparatuses have been proposed which seek to remove liquid solvent from the ink deposited onto the recording medium.
Japanese Patent Application Publication No. 10-86353 (see FIG. 9 in particular) discloses an image forming apparatus in which a heating device or halogen heater for heating the recording medium is disposed below a platen which opposes an ink droplet ejection head, in such a manner that the recording medium can be heated by means of the single halogen heater, before the image recording, during the image recording, and after the image recording.
Japanese Patent Application Publication No. 2001-179959 (see, in particular, FIG. 1 and paragraphs 0012 and 0013) discloses an image forming apparatus having a roller disposed after an ink droplet ejection head in the conveyance direction of the recording medium. The roller is constituted by a solvent absorbing medium that absorbs liquid solvent in the ink deposited on the recording medium, and a separating member having separating properties that any of the coloring material in the ink hardly adheres to the separating member.
However, if the solvent component on the recording medium is to be removed by heating the recording medium, then even supposing that the recording medium is heated before, during, and after the image recording, a long amount of time is still required from the deposition of the ink on the recording medium until complete drying of the recording medium, and the amount of power consumption required for heating of this kind is constantly high.
On the other hand, if it is sought to absorb the solvent component on the recording medium by means of a roller, then the roller inevitably makes contact with the coloring material and the like. Hence, a surplus external pressure is applied to the coloring material component that is to be fixed onto the recording medium, thereby causing disturbance of the image on the recording medium.
In the method described in Japanese Patent Application Publication No. 2001-179959, especially if the recording medium is a non-permeable medium, the coloring material is repelled by the separating member of the roller in a state where the coloring material is not yet fixed on the recording medium, and hence the image is disturbed. If the separation properties of the separating member in the roller are incomplete, or if a roller having an external surface made of a solvent absorbing member without a separating member of this kind is used, then the coloring material may adhere to the roller when it is sought to sufficiently remove the solvent component, and the image is ultimately disturbed.